Air cushion restraint inflator assembly

ABSTRACT

A gas generating device is disclosed which includes a substantially cylindrical outer sleeve defining groups of gas exit ports and a substantially cylindrical inner sleeve for containing a reactable gas-generating material defining groups of gas entrance ports with the inner sleeve being mounted generally coaxial to the outer sleeve. Annular side walls define a plurality of alternating first and second filter chambers in the annular space between the inner and outer sleeves. The first filter chambers are defined by adjacent pairs of annular side walls having a group of gas entrance ports therebetween and contain first filter means. The second filter chambers are defined by adjacent pairs of annular side walls having a group of gas exit ports therebetween and contain second filter means. The second filter chambers communicate with the first filter chambers by means of openings in the annular side walls. Means are provided for initiating reaction of the reactable gas generating material. The gas entrance ports and gas exit ports are so interleaved so as to permit the gas and particulate flow generated within the inner sleeve to follow azimuthal paths of substantially equal length from the entrance ports to the exit ports.

BACKGROUND OF THE INVENTION

This invention relates generally to devices capable of generatingsubstantial volumes of gas within a very brief time span, generally afew milliseconds. Gas generators of this type are used to inflate aircushion restraints of the type used in passive vehicle restraint systemsdesigned to insulate vehicle passengers from the harmful secondaryimpact effects of rapid deceleration caused by vehicle collisions. Onetechnique for inflating air cushion restraints is to connect a reservoirof gas in a cylinder under very high pressure to the air cushionrestraint. Upon receipt of a signal from a crash impact sensing devicean explosively actuated valve opens, releasing the gas from thecylinder. However, in order to obtain a sufficient volume of gas[approximately 10 cubic feet] for inflating the cushion restraint arelatively large reservoir of gas at pressures of 3,000 psi or more isrequired. The size of such a container creates difficult engineeringproblems, with regard to cylinder location, safety and vehicle balancerequirements. The compressed gas cylinder technique for inflating aircushion restraints suffers from the additional disadvantage in thatpressure is maximum at the commencement of the deployment of the aircushion and decreases as a function of time as the gas in the cylinderis depleted. Further, a minor leak in the cylinder can result in loss ofsubstantial amounts of gas by accidental discharge during the longperiod that the restraint system must remain in the vehicle. Thepressurized gas technique also results in substantial cooling of the gasas it expands thus reducing the effective available volume of gas. Thisrequires a total storage volume significantly greater than if the gaseswere at an elevated temperature and further adds to the above-discussedautomotive engineering problems.

Another technique for generating gas within the requisite short periodof time is the use of pyrotechnic charges to inflate air cushionrestraints. In such a device the inflating gas is generated by the rapidreaction of the charge reactants upon receipt of a signal from an impactsensing device. While pyrotechnic devices eliminate the problemsheretofore discussed which are associated with compressed air systems,the results of the required exothermic reaction, heat and by-products,must be controlled within acceptable limits for safe use. The gasesinflating the air cushion restraint must not have chemical or thermalcharacteristics which will undermine the mechanical strength of thecushion restraint itself or injure the passenger in the case of acushion restraint rupture. Therefore the generated gas flow, whichincludes a gas phase as well as a particular phase, must be cooled andfiltered within the generator before it enters into the air cushionrestraint. In addition, automobile manufacturers have further requiredthat such gas generating units must be nonpropulsive, that is, the gasescaping through the gas exit ports into the restraint cushion mustexert a net reactive force of approximately zero, to preclude what wouldotherwise be a dangerous condition in the event the generator becomesdetached from its mounting. In devices of this type the use ofmechanical filters utilizing fine screen to filter and cool the gasprior to its exit from the gas generator has been shown to be mosteffective. However, certain known devices using such mechanical filtersand conforming to the nonpropulsive requirement have heretofore beenprovided with a filter covering the gas exit ports of the combustorchamber that is radially and axially continuous from end to end. This isvery inefficient as it requires the use of a large amount of expensivescreen material. Further, such a construction prevents the use ofinterchangeable filter components which may be mass produced andassembled by relatively unskilled personnel thereby further increasingthe cost of each inflator unit. One such device comforming to thenonpropulsive requirement is in the form of concentrically mountedcylinders, with the outer cylinder having gas exit ports for directingflow into an inflatable bag. The gas exit port configuration isnecessarily limited to two rows of such ports each being on an oppositeside of the cylinder. Efficient operation of an inflator having such agas exit port configuration requires that the gas entrance ports of theinner cylinder, which functions as the combustion chamber, also belimited to two rows each being on an opposite side of the innercylinder. The rows are interleaved with and separate from the gas exitholes in the outer cylinder. This configuration requires a filter whichis radially and axially continuous to compensate for possible mechanicalstress on the filter means resulting from such a gas entrance and exitport configuration. If a continuous screen filter is not used inconjunction with the above structure it is difficult to seal the systemadequately to prevent unwanted by-products of the exothermic gasproducing reaction from bypassing the filter and reaching the restraintcushion. Also, a noncontinuous filter would be prone to displacementpossibly resulting in a pressure drop across the gas exit portshampering proper cushion deployment.

SUMMARY OF THE INVENTION

The present invention relates to a gas generating device in which thefilter means and the housing cooperate to provide the stability requiredfor preventing filter screen displacement, permitting the use ofsignificantly less screening material and resulting in substantialreduction of the production cost of each unit with no loss ofefficiency.

The air cushion restraint inflator assembly of the present inventioncomprises an elongated substantially cylindrical outer sleeve having aplurality of openings therein defining gas exit ports. The openings aredivided into a plurality of narrow bands of openings separated from oneanother in an axial direction along the length of the outer sleeve byportions of the outer sleeve which do not define openings. Each narrowband includes a plurality of openings spaced apart circumferentiallyabout the outer sleeve.

An elongated substantially cylindrical inner sleeve for containing areactable gas generating material is mounted generally coaxial to theouter sleeve and defines an annular region therebetween. The innersleeve has a plurality of openings defining first filter chamber gasentrance ports which are segregated into a plurality of narrow bands ofgas entrance ports. The bands of gas entrance ports are separated fromone another in an axial direction by portions of the inner sleeve whichdo not define openings. The bands of gas entrance ports are interleavedwith and separated from the bands of gas exit ports in an axialdirection. Each band includes a plurality of gas entrance ports spacedapart circumferentially about the inner cylindrical sleeve. Theinvention further includes means for initiating reaction of thereactable gas generating material.

A plurality of annular side walls extend between the inner and outersleeves and are separated from one another in an axial direction. Theside walls segment the annular region into a plurality of filterchambers, each annular side wall being positioned between a group of gasexit ports and a group of gas entrance ports. Alternating first annularfilter chambers are defined by adjacent pairs of annular side wallswhich have a group of gas entrance ports therebetween with each firstchamber including a first filter means. Alternating second annularfilter chambers are defined by adjacent pairs of annular side wallswhich have a group of gas exit ports therebetween with each secondchamber including a second filter means. The second filter chamberscommunicate with the first filter chambers by means of annular side wallopenings. In accordance with the invention the outer sleeve gas exitports are so interleaved with the inner sleeve gas entrance ports as topermit the gas and particulate flow generated within the inner sleeve tofollow azimuthal paths of substantially equal length from the gasentrance ports through the first and second annular filter chambers andout of the gas exit ports without bypassing the filter means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (comprised of FIG. 1A and FIG. 1B, broken along lines 1--1) is aside view shown partly in section of the air cushion restraint inflatorassembly of the present invention.

FIG. 2 is a cross-sectional view of the air cushion restraint inflatorassembly taken along lines 2--2 of FIG. 1.

FIG. 3 is a cross-sectional view of the air cushion restraint inflatorassembly taken along lines 3--3 of FIG. 1.

FIG. 4 is a cross-sectional view of the air cushion restraint inflatorassembly taken along lines 4--4 of FIG. 1.

FIG. 5 is a cross-sectional view of an alternate embodiment of the firstfilter chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The air cushion restraint inflator assembly 1 as shown in FIG. 1includes an elongated generally cylindrical outer sleeve 2 having aplurality of gas exit ports 3. The exit ports 3 are divided into aplurality of groups of exit ports 3', separated from one another in anaxial direction along substantially the entire length of the outersleeve 2. As shown in FIGS. 1, 2 and 3, each group includes multiplerows of openings. Each group 3' of openings extends about thecircumference of the outer sleeve in a narrow band. An elongatedcylindrical inner sleeve 4 is mounted coaxial to the outer sleeve withthe inner surface 2' of the outer cylinder and the outer surface 4' ofthe inner cylinder, defining an annular space 5 therebetween. The innersleeve 4 contains a reactable gas generating material in the form of aplurality of propellant wafers 6. The propellant is pressed into wafersto prevent the burning of significant amounts of propellant outside thecombustion chamber, to give a more constant gas generation rate and toprevent shifting of the propellant. Each wafer 6 is configured in amanner to allow space for propellant powder to be uniformally placedbetween the wafers, assuring a continuous propellant phase. This ensuresnear instantaneous ignition of all wafers, end to end, and cushions eachwafer from shock and vibration. The wafers may be enclosed in ahermetically sealed cartridge 7 made of a frangible material such as apolyamide film or a phenolic impregnated paper tube. The cylindricalinner sleeve 4 has a plurality of gas entrance ports 8 which aresegregated into a plurality of groups of entrance ports 8' separatedfrom one another in an axial direction and extending around the entirecircumference of the inner sleeve as shown in FIG. 4. Each group of gasentrance ports 8' is interleaved with and separated from the groups ofgas exit ports 3' in an axial direction. Means are located within theinner sleeve for initiating reaction of the gas generating wafers. Thisinitiating means is in the form of a squib 9 projecting into the innersleeve 4. The squib is responsive to intertial actuators (not shown)which detect rapid changes in vehicle velocity. Igniter end closure cap18 and closure cap 19 are secured to the inner and outer sleeves andindex the annular space 5. The igniter end closure cap houses the squib9 which is connected to the actuator by means of connector 20.

The annular space 5 is provided with a plurality of annular side walls10. Each annular side wall has an opening 10', positioned near the outersurface 4' of inner sleeve 4. The walls are separated from one anotherin an axial direction and segment the annular region into a plurality offilter chambers effectively sealing each filter chamber from the otherand preventing unwanted by-products from entering the restraint cushion.A first annular filter chamber 11 is defined by adjacent pairs ofannular side walls 10 which have a group of gas entrance ports 8'therebetween and a second annular filter chamber 12 is defined byadjacent pairs of annular side walls 10 which have a group of gas exitports 3' therebetween. The first annular filter chamber 11 communicateswith the second annular filter chamber 12 by means of the openings 10'.The side walls 10 are axially loaded against the outer sleeve 11' of thefirst filter 11 to affect a seal which prevents unwanted by-productsfrom bypassing the second filter and entering the restraint cushion.

If chemical agents such as adipic acid and aluminum sulfateoctadecahydrate are to be used to cool and neutralize the gas, they maybe placed either in the first filter chamber or the second filterchamber. FIG. 5 illustrates a preferred embodiment wherein a firstfilter chamber contains chemical agents supplementing the mechanicalfilter means 16. The filter chamber 11 has an annular shelf 13upstanding from each of the opposed wall surfaces defining the chamber11. Each of shelves 13 has a plurality of holes 14 and a radiallyoutwardly directed flanged end portion 15. The first filter means 16 inthe form of a plurality of layers of steel mesh screen 16' is mountedwithin the first filter chamber spaced apart from its associated groupof gas entrance ports 8'. This provides a flow path from entrance ports8 to annular side wall openings 10'. The radially outwardly directedflanged end portions 15 of the shelves 13 provide lateral stability forthe filter 16 and the shelves 13 position the chemical agents within thefilter chamber 11. As shown in FIG. 1, if the chemical agents are to beplaced in the second filter chamber 12 interspersed between screenlayers 17' of filter means 17, the first filter chamber 11 will containonly the mechanical filter means 16. Second filter chamber 12 has afilter means 17 comprised of layers of screen 17' having different meshsizes with the mesh sizes being arranged in order of decreasing meshsize in the direction of gas flow. The screen layers are positionedparallel to the inner sleeve 4 and substantially parallel to the gasflow passing through openings 10' from chamber 11.

The above-described inflator assembly constructed of interchangeablecomponent parts, may be assembled quickly and easily by relativelyunskilled personnel. Further, the components may be manufacturedindividually at the most convenient locations therefore and subsequentlyassembled, thus assuring that production costs will be kept to aminimum.

In the event of collision, the squib 9 ignites and bursts through afrangible section of the propellant cartridge 7 adjacent to the squibend. The propellant cartridge may be made of a phenolic impregnatedpaper tube. This ignites the powder optimally distributed between thepropellant wafers 6 substantially simultaneously which in turn ignitesthe propellant wafers 6. The propellant may, for example, be of acomposition disclosed in U.S. Pat. No. 3,895,098. The flow, containing agas phase and a particulate phase, will flow through gas entrance ports8 and into the first filter chamber 11 substantially perpendicularly tothe layers of mesh screen 16'. The major portion of the gas stream flowpasses through the first filter 16 with most of the particulate phase,largely molten metal in the case of the propellant of U.S. Pat. No.3,895,098, being deposited on the mesh screen layers 16'. The remainderof the flow makes a 90° turn and moves in the direction of the annularside wall openings 10'. If the chemical agents are to be located infilter chamber 11, as shown in FIG. 5, the flow makes a plurality of 90°turns after being subjected to the gas cleaning action of the firstfilter means and passes through the shelf openings 14 after contactingthe chemical agents, making a last 90° turn before rejoining the otherflow portion. If the chemical agents are to be placed in filter chamber12, chamber 11 will house filter 16 only and the gas flow, after beingsubjected to the mechanical filtering process, makes a plurality ofturns of at least 90° and rejoins the other flow portion. The entire gasstream passes through the annular side wall openings 10' and enters thesecond filter chambers 12 contacting the mesh layers 17' of the secondfilter means 17 normal to the mesh layers. This ensures that the gasflow when it is at its highest velocity after the initial filtering willcontact the second filter means at its most stable point. The gas flowsthrough the second filter means 17, depositing any remaining particulatematter onto the mesh screen layers 17', out of the gas exit ports, andinto the restraint cushion (not shown). Throughout the first and secondfiltering phases, displacement of the filter members is inhibited by theannular side walls 10. As shown in FIGS. 2, 3 and 4, the filter systemis further stabilized by the interleaving of the gas entrance ports 8and the gas exit ports 3. For example, a gas flow from gas entrance port8" shown in FIG. 4 follows a specific path to its associated gas exitports 3" shown in FIGS. 2 and 3. A gas flow from entrance port 8''',also shown in FIG. 4, to its associated gas exit ports 3''' will followan azimuthal path of substantially the same length. This reduces stresson the filter screens thereby minimizing filter displacement which wouldcause a pressure drop across the groups of exit ports 3', possiblyinterfering with proper cushion deployment.

I claim:
 1. An air cushion restraint inflator assembly comprising:(a) anelongated substantially cylindrical outer sleeve having a plurality ofopenings therein defining gas exit ports, the openings being dividedinto a plurality of narrow bands of openings separated from one anotherin an axial direction along the length of the outer sleeve by portionsof the outer sleeve which do not define openings, each narrow bandincluding a plurality of openings spaced apart circumferentially aboutthe outer sleeve; (b) an elongated substantially cylindrical innersleeve mounted within and in generally coaxial relation to the outersleeve and for containing a reactable gas-generating material, saidinner and outer sleeves defining an annular region therebetween, saidinner sleeve having a plurality of openings defining first filterchamber gas entrance ports segregated into a plurality of narrow bandsof gas entrance ports, the bands of gas entrance ports being separatedfrom one another in an axial direction by portions of the inner sleevewhich do not define openings and interleaved with, and separted from thebands of gas exit ports in an axial direction, each narrow bandincluding a plurality of gas entrance ports spaced circumferentiallyabout the inner cylindrical sleeve; (c) means for initiating reaction ofthe reactable gas generating material; and (d) a plurality of annularside walls extending between the inner and outer sleeves and separatedfrom one another in an axial direction to segment the annular regioninto a plurality of filter chambers, each annular side wall beingpositioned between a group of gas exit ports and a group of gas entranceports thereby forming alternating:(1) first annular filter chambersdefined by adjacent pairs of annular side walls which have a group ofgas entrance ports therebetween each first chamber including a firstfilter means, and (2) second annular filter chambers defined by adjacentpairs of annular side walls which have a group of gas exit portstherebetween each second chamber including a second filter means, saidsecond filter chambers communicating with said first filter chambers bymeans of annular side wall openings.
 2. The air cushion restraintinflator assembly according to claim 1 wherein the openings definingsecond filter chamber gas exit ports are substantially circular.
 3. Theair cushion restraint inflator assembly according to claim 2 wherein theopenings defining first filter chamber gas entrance ports aresubstantially circular.
 4. The air cushion restraint inflator assemblyaccording to claim 3 wherein the annular side wall openings arepositioned proximal the inner sleeve and are defined by the radiallyinnermost surfaces of the annular side walls and the correspondingopposing inner sleeve outer wall portion
 6. 5. The air cushion restraintinflator assembly according to claim 4 wherein the outer sleeve gas exitports are so interleaved with the inner sleeve gas entrance ports as topermit the gas and particulate flow generated within the inner sleeve tofollow azimuthal paths of substantially equal length from the gasentrance ports, through the first and second annular filter chambers andout of the gas exit ports thereby maintaining the mechanical seal andintegrity of the first and second filter means and providing for uniformfiltration of the gas and particulate flow.
 6. The air cushion restraintassembly according to claim 5 wherein the first filter means iscomprised of a plurality of layers of mesh screen mounted radiallyspaced apart from the gas entrance port and substantially perpendicularto the flow of gas from the gas exit port, with the bottom screen layerof the filter means and the outer surface of the inner sleeve defining apassage from the gas entrance port to the annular side wall openingsassociated therewith.
 7. The air cushion restraint inflator assemblyaccording to claim 6 further comprising an annular shelf upstanding fromeach of the opposed wall surfaces of the first filter chambers proximalto and outwardly disposed from the annular side wall openings, each ofsaid shelves defining a plurality of holes and having a radiallyoutwardly directed flanged end portion said flanged end portionsproviding support for filter means disposed therebetween.
 8. The aircushion restraint inflator assembly according to claim 7 wherein thesecond filter means includes a plurality of layers of screens positionedparallel to the inner sleeve with the mesh size of the screen layersdecreasing in the direction of gas flow, said filter being mountedwithin the chamber in such manner that the gas flow entering the secondfilter chamber contacts the initial filter screen portion edge on andparallel to the screen thereby subjecting the second filter means tohigh flow stress at its strongest point.
 9. The air cushion restraintinflator assembly according to claim 8 further including chemical agentsfor cooling and neutralizing the gas interspersed between the outerscreen layers of the second filter means.
 10. The air cushion restraintinflator assembly according to claim 9 wherein the chemical agentsinclude adipic acid and aluminum sulfate octadecahydrate.